Binary hydrides classification and general properties

Detailed chemistries of most of the hydrides are considered in later chapters. 

The four major classes into which it is convenient to place binary hydrides are  

Hydrogen atoms are small enough to occupy the interstitial holes in a metal lattice and the absorption of H2 by a variety of metals (and also alloys) leads to the formation of metal hydrides in which hydrogen atoms reside in interstitial cavities, interstitial metal hydrides. For example, non-stoichiometric hydrides TiHj 7, HfHi gg and HfH2.io are formed when titanium and hafnium react with H2. Niobium forms a series of non-stoichiometric hydrides of formula 

NbH (0 X 1) and at low hydrogen content, the bcc structure of Nb metal is retained. An interesting property of these metal hydrides is their ability to release hydrogen upon heating, and this leads to their use as hydrogen storage vessels (see the bar chart in Box 9.2). 

A number of hydrides fall into intermediate or borderline categories. 

The battery recycles hydrogen back and forth between anode and cathode, and can be charged and discharged 

Hybrid electric vehicles (HEV) such as the Toyota Prius, Honda Insight and Honda Civic Hybrid combine a conventional internal combustion engine with a battery-powered motor (see also the discussion at the end of Box 10.2). Nickel-metal hydride batteries are routinely applied in hybrid electric vehicles, although there is increasing competition from 

Cut away model of the Toyota Prius hybrid saloon car at the 2009 Frankfurt Motor Show. 

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Chapter 9 Binary hydrides classification and general properties 251... 

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